Coating metal articles



Patented Dec. 9, 1930 UNITED STATES PATENT OFFICE FREDERICK M. BECKET, OF NEW YORK, N. Y., ASSIGNOR TO ELECTRO METALLURGICAL COMPANY, A CORPORATION OF WEST VIRGINIA COATING METAL ARTICLES No Drawing.

The invention relates to processes for modifying the surfaces of metal articles by cementation. Examples of processes of this type are those known commercially .as-

sherardizing, calorizin and chromiz ing. In a process covere in my Patent No.

1,672,444, dated June 5, 1928, both silicon and chromium are introduced into the surface of a metal article to form a corrosion-resistant layer. The present invention is especially adapted to be used in connection with the process of that patent, but it is applicable to other coating or casing processes of the cementation type.

In cementation coating processes'it is customary to incorporate into the cementation mixture a fiuxing substance designed to expedite and regulate the formation of the desired coating. Such fluxing substances are sometimes called energizers. Ammonium chloride has been Widely and successfully used for this purpose. Zinc chloride has also been used.-

I have discovered that the use of a silico fluoride or fluosilicate as an energizer, for

example the sodium salt, N21 SiF gives superior results, especially where silicon is to be incorporated into the surface coating. The silicofluoride gives a high rate of mix gration, and as compared with known energizers it often gives a denser and more c0- herent coating with a smoother and more uniform surface. At the higher cementation temperatures, ammonium chloride, zinc chloride and like energizers volatilize rapidly, displacing the cementation mixture with the result that contact is destroyed between the mixture and the article under treatment, and oxidizing gases, if present, are permitted to penetrate the mixture and to act on the surface to be coated. The silicofluorides, on the contrary, are practically non-volatile at the temperatures involved, and hence avoid the difficulties just described.

The use of a silicofluoride energizer re- Application filed October 29, 1928. Serial No. 315,931.

quires no change with respect to the other constituents of the mixture. Excellent results have been had using a mixture containing powdered iron-chromium-silicon alloy parts; alumina 45 parts; and sodium silicofluoride 2.5 parts. The alloy contained approximately Cr 40% and Si 20%. As in the case of other energizers the action of the silicofluoride is analogous to that of a catalyst, and the proportion used is not a matter 55 of great importance. Merely by way of example it may be stated that a proportion of silicofluoride between 0.5% and 10% is suitable, but a useful efl'ect can undoubtedly be obtained with a content outside this range.

In the appended claims, the term metal designates a substance having metallic characteristics and containing one or more chemical elements. Silicon for the purposes of this application, is classified as a metal. Where the claims recite silicon as a constituent of a cementation mixture, it will be understood that so-called metallicsilicon or its alloys or silicides is meant.

I claim 1. A cementation mixture comprising a silicofluoride and a corrosion-resisting metal.

2. A cementation mixture comprising a silicofluoride and silicon.

3. A cementation mixture comprising a 7 silicofluoride and an alloy containing chromium and silicon.

4. A cementationmixture comprising 0.5% to 10% of sodium silicofluoride and an alloy containing iron, chromium and silicon.

5. The process of forming a coating on a ferrous article which comprises heating the article in contact with a mixture containing a silicofluoride and a corrosion-resisting metal until cementation occurs.

6. The process of forming a coating on a ferrous article which comprises heating the article in contact with a mixture containing a silicofluoride and silicon until cementation occurs.

7 The process of forming a coating on a ferrous article which comprises heating the article in contact with a mixture containing a silicofluoride and an alloy containing chr0- mium and silicon until cementation occurs.

8. The process of forming a coating on a ferrous article which comprises heating the article in contact with a mixture containing a silicofiuoride and an alloy containing iron, chromium and silicon until cementation occurs.

In testimony whereof, I afiix my signature.

FREDERICK M. BECKET. 

